X can do a piece of work in 40 days. He works at it for 8 days and then Y finishes it in 16 days. How long will they together take to complete the work?

Work done by X in 8 days = 1/40×8 = 1/5

Remaining work = 1−1/5 = 4/5

Now, 4/5 work is done by Y in 16 days
Whole work will be done by Y in = 16×5/4 = 20 days
∴ X's 1 day's work = 1/40

∴ Y's 1 day's work = 1/20

(X + Y)'s 1 day's work
=1/40 + 1/20
=3/40

Hence, X and Y will together complete the work in
= 40/3
= 13(1/3) days